A wide variety of therapeutic techniques have been developed to correct or inhibit vascular diseases. Coronary artery disease (CAD), for example, is an adverse condition of the heart in which the blood flow to the heart muscle is partially or totally restricted by occlusive material in the coronary arteries is which narrows the blood flow lumen. The occlusive materials deprive portions of the heart muscle of essential oxygenated blood.
CAD may be treated by a surgical technique referred to as coronary artery bypass graft (CABG) surgery. This surgical procedure involves supplementing blood flow to the heart muscle by grafting non-native conduit such as a saphenous vein graff (SVG) to the heart. A first end of the SVG is connected to the ascending aorta (proximal to the occlusive material) and the other end is connected to the artery distal of the occlusive material. Although this technique has been useful for treating CAD in native coronary arteries, it is not uncommon for occlusive material to form over time in the SVG thereby necessitating additional therapy. Typically, the nature of the occlusive material in the new SVG may be diffuse, friable, grumous-like, paste-like, granular, and/or chunky.
Percutaneous translumenal coronary angioplasty (PTCA) has gained wide acceptance as an effective and less invasive alternative to CABG surgery in certain patient groups. The PTCA procedure involves the use of an angioplasty balloon catheter, several types of which are well known in the art. The balloon catheter is inserted into the body via the femoral artery and navigated to the coronary arteries assisted by a guide catheter and (usually) a guide wire. The balloon is positioned across the restriction in the artery and subsequently inflated. The inflated balloon widens the restriction and restores blood flow to portions of the heart muscle previously deprived of oxygenated blood.
Although balloon PTCA has been demonstrated to be clinically effective in treating a wide variety of vascular restrictions, there are alternative devices and techniques which are specially adapted to treat lesions with complex morphology and/or unique pathology. For example, SVGs commonly contain abnormal deposits which are diffuse, degenerated, and thrombus-containing. Because treating an SVG lesions with balloon PTCA has an unfavorably high incidence of distal embolization, alternative therapies such as atherectomy have been favored.
Atherectomy (or thrombectomy) is an alternative to balloon PTCA and targets specific types of lesion morphology and pathology. Atherectomy, as distinguished from balloon PTCA, removes the occlusive material from the local vasculature rather than molding or reshaping the restriction by compression. While some prior art atherectomy devices have been specifically indicated to be effective for treating certain types of diseased SVGs, the incidence of complications (e.g. distal coronary artery embolization, cerebral embolization via the aorta) has been reported to be sub-optimally high. Thus, there is a need for an improved atherectomy or thrombectomy device for the removal occlusive material, particularly in friable, diffusely diseased SVGs.
Several prior art atherectomy or thrombectomy devices utilize concepts of fluid jets to remove occlusive material. For example, EPO Application 470,781 A1 to Drasler discloses a device which uses high pressure water jets to remove occlusive material. The high pressure water jet is directed proximally to dislodge and emulsify thrombus. However, because of the high pressures associated with this device and the corresponding risk of damage to the vessel wall if exposed to the high pressure jet, the water jet is only exposed through a laterally facing window in a protective housing. Since the effective cutting area is limited to the size of the window, multiple passes are required to remove occlusive material deposited around the inner circumference of the vessel. Furthermore, because the device utilizes a prospective housing, a portion of the device must first traverse the occlusion before the water jet is able to dislodge and emulsify the occlusive material. This unnecessarily increases the risk of distal embolization and increases the difficulty in crossing a tight occlusion.
A similar high pressure water jet atherectomy device is disclosed in EPO Application 485,133 A1 to Drasler. This water jet atherectomy device also utilizes a very high pressure (more than 3,500 psi) water jet which is directed distally or proximally within a protective housing. This device further includes a biasing balloon which permits asymmetric or directional atherectomy. Once again, because of the high pressures associated with this device and the corresponding risk of damage to the vessel wall if exposed to the high pressure, the cutting area is essentially limited to the open window in the protective housing. Since the effective cutting area is limited to the size of the window, multiple passes are required to remove occlusive material deposited around the inner circumference of the vessel. Furthermore, because the device utilizes a protective housing, a portion of the device must first traverse the occlusion before the water jet is able to dislodge and emulsify the occlusive material. As stated earlier, this unnecessarily increases the risk of distal embolization and increases the difficulty in crossing a tight occlusion.
A further example of a high pressure water jet atherectomy device is disclosed in EPO Application 489,496 A1 to Drasler. This water jet atherectomy device also utilizes a very high pressure (more than 3,500 psi) water jet directed distally to dislodge and emulsify thrombus. The jet stream is directed distally to permit the ablation of a total occlusion without requiring the distal end of the device to first cross the occlusion. However, because of the distally directed high pressure water jet used in this device, damage to the vessel wall is risked for lack of a protective shield. Furthermore, the distally directed water jet tends to flush the dislodged material in a distal direction which may result in undesirable embolization.
Another pressurized (440 psi minimum pressure source) fluid device is disclosed in U.S. Pat. No. 4,690,672 to Veltrup. This device directs a fluid stream proximally into a mouth of a suction tube and removes unwanted material when the material is in juxtaposition with the mouth of the suction tube. Similar disadvantages are associated with this device. For example, the cutting diameter is essentially limited to the size of the opening, which is less than the diameter of the catheter shaft. Additionally, no occluding balloon is provided which increases the risk of simply draining blood from the occluded vessel. Also, no guide wire is provided to guide the catheter within the vasculature, thus intravascular navigation would be significantly limited.
A further limitation common to several of the above-cited fluid jet atherectomy devices is that the fluid input lumen and the effluent lumen are longitudinally fixed relative to each other. More specifically, the fluid input lumen and the effluent lumen can not be longitudinally moved independently. This requires the relatively large effluent lumen to be advanced along with the fluid input lumen. Since the effluent lumen is relatively large and stiff, the distance the device can be advanced into tortuous and/or small diameter vessels is limited. Additionally, the fluid input lumen can not be retracted into the extraction lumen to clean up clogging debris.
In view of the unresolved disadvantages of each of these devices, it is desirable to have a device which utilizes a relatively low fluid pressure to minimize the risk of causing damage to the vessel wall. It is also desirable to have a device which directs fluid laterally rather than proximally or distally. Laterally directed fluid allows the device to dislodge material immediately adjacent the distal end of the device without first traversing the occlusion and also reduces the risk of distal embolization. It is further desirable to have a device which utilizes independently movable fluid input and fluid extraction lumens to maximize vascular accessibility and remove clogs that form in the extraction lumen.